DC Generator MCQ Questions and Answers for Electrical Engineering Exams

Search Description: Practice 150+ DC generator MCQs with answers and explanations for electrical engineering, diploma, ITI, GATE, SSC JE, RRB JE and interview preparation.

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Introduction

DC Generator is one of the most important topics in Electrical Machines. In simple words, a DC generator converts mechanical energy into direct current electrical energy with the help of electromagnetic induction. Questions from this topic are commonly asked in semester exams, electrical engineering objective tests, technical interviews and government job exams.

In this article, you will get more than 150 DC Generator MCQ questions with answers and short explanations. The questions are arranged from easy to hard so that beginners can first understand the basics and then move to numerical, winding, commutation, armature reaction and performance-based questions.

Table of Contents

1. Quick Notes on DC Generator
2. Easy DC Generator MCQs
3. Intermediate DC Generator MCQs
4. Advanced DC Generator MCQs
5. Quick Answer Key
6. Frequently Asked Questions

Quick Notes on DC Generator

• A DC generator works on Faraday’s law of electromagnetic induction.
• Fleming’s right-hand rule is used to find the direction of induced emf.
• The armature core is laminated to reduce eddy current loss.
• The commutator works like a mechanical rectifier.
• Brushes collect current from the commutator and deliver it to the external load.
• Armature reaction distorts and weakens the main magnetic field.
• Interpoles and compensating windings improve commutation and reduce sparking.

Easy DC Generator MCQs

These beginner-level questions cover basic construction, working principle and important parts of a DC generator.

1. DC generator converts mechanical energy into:

1. Heat energy
2. DC electrical energy
3. Chemical energy
4. Light energy

Answer: B. DC electrical energy

Explanation: A DC generator works as an electromechanical energy converter and gives DC output.

2. The working principle of a DC generator is based on:

1. Ohm’s law
2. Faraday’s law of electromagnetic induction
3. Coulomb’s law
4. Lenz’s law only

Answer: B. Faraday’s law of electromagnetic induction

Explanation: When conductors cut magnetic flux, emf is induced according to Faraday’s law.

3. The direction of induced emf in a DC generator is found by:

1. Fleming’s left-hand rule
2. Fleming’s right-hand rule
3. Right-hand thumb rule
4. Cork screw rule

Answer: B. Fleming’s right-hand rule

Explanation: Fleming’s right-hand rule is used for generator action.

4. The stationary part of a DC machine is called:

1. Rotor
2. Stator
3. Armature
4. Commutator

Answer: B. Stator

Explanation: The stator is the fixed part carrying the field system.

5. The rotating part of a DC generator is generally:

1. Yoke
2. Pole shoe
3. Armature
4. Brush

Answer: C. Armature

Explanation: The armature rotates and cuts magnetic flux to generate emf.

6. The outer frame of a DC machine is known as:

1. Yoke
2. Commutator
3. Armature core
4. Brush holder

Answer: A. Yoke

Explanation: The yoke gives mechanical support and provides a path for magnetic flux.

7. Field winding in a DC generator is used to produce:

1. Mechanical torque
2. Magnetic field
3. Eddy current
4. Friction

Answer: B. Magnetic field

Explanation: Field winding produces the main magnetic flux.

8. Field coils are generally made of:

1. Mica
2. Copper
3. Cast iron
4. Carbon

Answer: B. Copper

Explanation: Copper is preferred because of its good electrical conductivity.

9. The armature core is laminated to reduce:

1. Copper loss
2. Eddy current loss
3. Mechanical loss
4. Brush loss

Answer: B. Eddy current loss

Explanation: Laminations increase resistance to eddy current paths and reduce iron loss.

10. Laminations of armature core are commonly made of:

1. Silicon steel
2. Wood
3. Aluminium only
4. Plastic

Answer: A. Silicon steel

Explanation: Silicon steel reduces hysteresis loss and supports magnetic flux.

11. The commutator in a DC generator acts as a:

1. Transformer
2. Mechanical rectifier
3. Fuse
4. Capacitor

Answer: B. Mechanical rectifier

Explanation: It converts the alternating emf in armature into unidirectional output.

12. Brushes are used to collect current from:

1. Yoke
2. Pole shoe
3. Commutator
4. Shaft

Answer: C. Commutator

Explanation: Brushes maintain sliding contact with the commutator.

13. Brushes in DC machines are usually made of:

1. Wood
2. Carbon or graphite
3. Glass
4. Rubber

Answer: B. Carbon or graphite

Explanation: Carbon/graphite brushes provide good contact and lower wear.

14. Pole shoes are used mainly to:

1. Increase speed
2. Spread flux uniformly
3. Reduce shaft weight
4. Store charge

Answer: B. Spread flux uniformly

Explanation: Pole shoes support field coils and distribute flux over the air gap.

15. The prime mover of a DC generator supplies:

1. Electrical input
2. Mechanical input
3. Chemical input
4. Magnetic input

Answer: B. Mechanical input

Explanation: A prime mover rotates the generator shaft mechanically.

16. Generated emf in a DC generator is directly proportional to:

1. Speed only
2. Flux only
3. Flux and speed
4. Resistance only

Answer: C. Flux and speed

Explanation: EMF increases with both flux per pole and speed.

17. The air gap in a DC machine is between:

1. Brush and commutator
2. Pole shoe and armature
3. Yoke and shaft
4. Bearing and frame

Answer: B. Pole shoe and armature

Explanation: The armature rotates inside the pole shoes with a small air gap.

18. In generator action, conductor motion through magnetic field produces:

1. Induced emf
2. Only heat
3. Only friction
4. No voltage

Answer: A. Induced emf

Explanation: Cutting of magnetic flux produces induced emf.

19. The material used for commutator segments is generally:

1. Copper
2. Mica
3. Cast iron
4. Steel

Answer: A. Copper

Explanation: Copper is used for good conductivity.

20. The insulation between commutator segments is usually:

1. Oil
2. Mica
3. Paper only
4. Lead

Answer: B. Mica

Explanation: Mica provides strong electrical insulation between segments.

21. A DC generator output is taken from:

1. Field winding only
2. Brushes
3. Yoke
4. Bearings

Answer: B. Brushes

Explanation: Brushes connect the rotating commutator to the external circuit.

22. The main flux in a DC generator is produced by:

1. Armature winding
2. Field poles
3. Commutator
4. Brushes

Answer: B. Field poles

Explanation: Field poles carry field coils and create the main magnetic field.

23. A separately excited DC generator has field winding supplied from:

1. Its own armature only
2. An external DC source
3. AC supply only
4. No source

Answer: B. An external DC source

Explanation: In separately excited machines, field current comes from an independent DC source.

24. A self-excited generator uses:

1. Residual magnetism
2. Transformer action
3. Capacitor starting only
4. AC excitation only

Answer: A. Residual magnetism

Explanation: Residual magnetism helps build voltage when the field is connected to its own output.

25. A shunt generator field winding is connected:

1. In series with load
2. In parallel with armature
3. Only across brush contact
4. Open circuit

Answer: B. In parallel with armature

Explanation: Shunt field has many turns and is connected across the armature terminals.

26. A series generator field winding is connected:

1. In parallel with load
2. In series with armature and load
3. Across supply separately
4. Not connected

Answer: B. In series with armature and load

Explanation: Series field carries load current.

27. Compound generators have:

1. Only shunt field
2. Only series field
3. Both series and shunt fields
4. No field winding

Answer: C. Both series and shunt fields

Explanation: Compound generators combine series and shunt excitation.

28. Cumulative compound generator means series field:

1. Opposes shunt field
2. Assists shunt field
3. Is disconnected
4. Produces zero flux

Answer: B. Assists shunt field

Explanation: In cumulative compounding, the series field strengthens the shunt field.

29. Differential compound generator means series field:

1. Assists shunt field
2. Opposes shunt field
3. Has no current
4. Acts as armature

Answer: B. Opposes shunt field

Explanation: Here the series flux opposes the shunt flux.

30. The emf equation of DC generator is:

1. E = PΦZN/60A
2. E = VI
3. E = IR
4. E = mc²

Answer: A. E = PΦZN/60A

Explanation: Generated emf depends on poles, flux, conductors, speed and parallel paths.

31. In the emf equation, Φ represents:

1. Flux per pole
2. Frequency
3. Current
4. Resistance

Answer: A. Flux per pole

Explanation: Φ is the magnetic flux produced per pole.

32. In the emf equation, Z represents:

1. Number of poles
2. Number of armature conductors
3. Speed
4. Parallel paths

Answer: B. Number of armature conductors

Explanation: Z is the total number of armature conductors.

33. In the emf equation, A represents:

1. Area of yoke
2. Parallel paths in armature
3. Armature current
4. Air gap

Answer: B. Parallel paths in armature

Explanation: A is the number of parallel paths in armature winding.

34. For simplex lap winding, number of parallel paths is:

1. 2
2. P
3. P/2
4. 1

Answer: B. P

Explanation: In simplex lap winding, A equals number of poles P.

35. For simplex wave winding, number of parallel paths is:

1. 2
2. P
3. P/2
4. P²

Answer: A. 2

Explanation: A simplex wave winding has two parallel paths.

36. Lap winding is generally suitable for:

1. High voltage, low current
2. Low voltage, high current
3. Only AC machines
4. No-load operation

Answer: B. Low voltage, high current

Explanation: Lap winding gives more parallel paths, so it is suitable for high current.

37. Wave winding is generally suitable for:

1. Low voltage, high current
2. High voltage, low current
3. Only transformers
4. Only motors

Answer: B. High voltage, low current

Explanation: Wave winding has fewer parallel paths, giving higher voltage.

38. Armature resistance drop is represented as:

1. IaRa
2. V/I
3. ΦN
4. PZ

Answer: A. IaRa

Explanation: Voltage lost in armature winding is armature current times armature resistance.

39. Terminal voltage of a loaded generator is less than generated emf due to:

1. Voltage drops
2. Zero resistance
3. No current
4. Perfect commutation

Answer: A. Voltage drops

Explanation: Internal drops such as armature resistance and brush drop reduce terminal voltage.

40. Armature reaction is caused by:

1. Field current only
2. Armature current
3. Yoke material only
4. Bearing friction

Answer: B. Armature current

Explanation: Load current in armature conductors produces armature flux.

41. The effect of armature reaction is to:

1. Only increase flux
2. Distort and weaken main flux
3. Stop rotation instantly
4. Remove losses

Answer: B. Distort and weaken main flux

Explanation: Armature reaction distorts the main field and may reduce effective flux.

42. The magnetic neutral axis shifts due to:

1. Armature reaction
2. Bearing lubrication
3. Yoke weight
4. Cooling fan

Answer: A. Armature reaction

Explanation: Armature reaction shifts the neutral zone under load.

43. Brushes are ideally placed along:

1. Magnetic neutral axis
2. Shaft axis
3. Yoke surface
4. Pole center only

Answer: A. Magnetic neutral axis

Explanation: At MNA, emf in the coil undergoing commutation is minimum.

44. Commutation means:

1. Conversion of AC supply to DC supply by transformer
2. Reversal of current in a coil under brush
3. Increasing speed
4. Reducing field current only

Answer: B. Reversal of current in a coil under brush

Explanation: During commutation, current in the short-circuited coil reverses.

45. Poor commutation generally causes:

1. Sparking at brushes
2. No friction
3. Perfect DC output
4. Zero losses

Answer: A. Sparking at brushes

Explanation: Incomplete current reversal leads to sparking.

46. Interpoles are used to improve:

1. Cooling only
2. Commutation
3. Shaft strength
4. Yoke weight

Answer: B. Commutation

Explanation: Interpoles neutralize reactance voltage and improve commutation.

47. Interpoles are connected in series with:

1. Armature
2. Shunt field only
3. Yoke
4. Bearings

Answer: A. Armature

Explanation: They must carry armature current so their effect changes with load.

48. Compensating windings are placed in:

1. Armature slots
2. Pole faces
3. Shaft
4. Bearings

Answer: B. Pole faces

Explanation: They are embedded in pole faces to counter armature reaction.

49. Compensating winding is mainly used in:

1. Small machines only
2. Large machines with heavy load changes
3. Only transformers
4. Only AC motors

Answer: B. Large machines with heavy load changes

Explanation: It helps reduce field distortion in large DC machines.

50. Eddy current loss can be reduced by:

1. Using solid iron core
2. Using laminated core
3. Increasing core thickness
4. Removing insulation

Answer: B. Using laminated core

Explanation: Thin insulated laminations limit circulating currents.

Intermediate DC Generator MCQs

These questions cover types of DC generators, winding, voltage build-up, losses, efficiency, armature reaction and characteristics.

1. Hysteresis loss depends mainly on:

1. Magnetic material and flux density
2. Brush pressure only
3. Load resistance only
4. Shaft diameter only

Answer: A. Magnetic material and flux density

Explanation: Hysteresis loss is related to repeated magnetization of iron.

2. Copper loss occurs due to:

1. Resistance of windings
2. Magnetic leakage only
3. Bearing movement only
4. Air friction only

Answer: A. Resistance of windings

Explanation: Current flowing through winding resistance produces I²R loss.

3. Mechanical losses include:

1. Friction and windage
2. Field copper loss
3. Armature copper loss
4. Eddy current loss

Answer: A. Friction and windage

Explanation: Mechanical rotation causes bearing friction and air windage losses.

4. Iron losses are also called:

1. Core losses
2. Brush losses
3. Stray load losses only
4. Mechanical losses

Answer: A. Core losses

Explanation: Hysteresis and eddy current losses occur in the iron core.

5. The efficiency of a DC generator is:

1. Output/Input
2. Input/Output
3. Loss/Input
4. Voltage/Current

Answer: A. Output/Input

Explanation: Efficiency is useful output power divided by input power.

6. Maximum efficiency occurs when variable loss is equal to:

1. Constant loss
2. Zero loss
3. Input power
4. Output voltage

Answer: A. Constant loss

Explanation: For maximum efficiency, variable copper loss equals constant loss.

7. Voltage regulation of a DC generator indicates change in:

1. Speed only
2. Terminal voltage from no-load to full-load
3. Weight
4. Frequency

Answer: B. Terminal voltage from no-load to full-load

Explanation: Voltage regulation measures how terminal voltage changes with load.

8. A good generator has:

1. High voltage regulation value always
2. Low voltage drop and good regulation
3. Zero output
4. No magnetic field

Answer: B. Low voltage drop and good regulation

Explanation: Less voltage change under load is generally desirable.

9. No-load characteristic of a DC generator is also called:

1. Open circuit characteristic
2. Short circuit test
3. Load test only
4. Brake test

Answer: A. Open circuit characteristic

Explanation: OCC shows generated emf versus field current at constant speed.

10. OCC is taken at:

1. Constant speed
2. Variable frequency only
3. Zero speed
4. Short circuit armature

Answer: A. Constant speed

Explanation: Speed is kept constant while field current is varied.

11. Residual magnetism is important in:

1. Self-excited generator voltage build-up
2. Transformer cooling
3. Brush wear only
4. Bearing design

Answer: A. Self-excited generator voltage build-up

Explanation: Without residual magnetism, voltage build-up may not start.

12. Critical field resistance is related to:

1. Voltage build-up in shunt generator
2. Armature slot shape only
3. Brush material only
4. Yoke painting

Answer: A. Voltage build-up in shunt generator

Explanation: Above critical resistance, a shunt generator may fail to build voltage.

13. Critical speed is the minimum speed for:

1. Voltage build-up at given field resistance
2. Reducing friction to zero
3. Removing copper loss
4. Breaking commutator

Answer: A. Voltage build-up at given field resistance

Explanation: Below critical speed, the generator may not excite properly.

14. A DC shunt generator may fail to build voltage if:

1. Residual magnetism is lost
2. Speed is correct
3. Field polarity aids residual flux
4. Field resistance is low

Answer: A. Residual magnetism is lost

Explanation: Voltage build-up needs residual magnetism and correct field connection.

15. If shunt field connection is reversed accidentally:

1. Voltage may not build up
2. Efficiency becomes 100%
3. Speed becomes zero always
4. Commutator disappears

Answer: A. Voltage may not build up

Explanation: Field flux may oppose residual magnetism, preventing build-up.

16. Open circuit characteristic initially starts from small voltage because of:

1. Residual magnetism
2. Full-load current
3. Brush friction
4. Armature reaction only

Answer: A. Residual magnetism

Explanation: Residual flux induces a small initial voltage.

17. Internal characteristic of a generator is between:

1. Generated emf and armature current
2. Terminal voltage and field current only
3. Speed and torque only
4. Resistance and temperature only

Answer: A. Generated emf and armature current

Explanation: It considers generated emf variation with load current.

18. External characteristic is between:

1. Terminal voltage and load current
2. Flux and speed only
3. Yoke size and current
4. Friction and speed only

Answer: A. Terminal voltage and load current

Explanation: It shows output terminal voltage as load current changes.

19. In a shunt generator, terminal voltage usually falls with load due to:

1. Armature drop and armature reaction
2. Increase in residual magnetism
3. Zero current
4. No losses

Answer: A. Armature drop and armature reaction

Explanation: Voltage falls because of internal drops and weakened flux.

20. Series generator terminal voltage initially rises with load because:

1. Series field flux increases
2. Speed becomes zero
3. Commutator opens
4. Armature resistance vanishes

Answer: A. Series field flux increases

Explanation: Load current strengthens series field until saturation.

21. After saturation in a series generator, voltage may drop because of:

1. Armature resistance drop
2. No load current
3. Zero flux
4. No commutation

Answer: A. Armature resistance drop

Explanation: At high current, internal voltage drops dominate.

22. Compound generator is used to get:

1. Better voltage regulation
2. Only zero voltage
3. Only AC output
4. No field flux

Answer: A. Better voltage regulation

Explanation: Compounding helps maintain terminal voltage with load.

23. Over-compounded generator gives full-load voltage:

1. Higher than no-load voltage
2. Always zero
3. Lower than no-load always
4. Same as speed

Answer: A. Higher than no-load voltage

Explanation: Extra series field raises voltage above no-load value.

24. Flat-compounded generator gives:

1. Nearly constant terminal voltage
2. Zero current
3. Only decreasing voltage
4. No output

Answer: A. Nearly constant terminal voltage

Explanation: It is designed to maintain almost constant voltage from no-load to full-load.

25. Under-compounded generator gives full-load voltage:

1. Less than no-load voltage
2. Greater than no-load voltage
3. Infinite voltage
4. No relation

Answer: A. Less than no-load voltage

Explanation: Series field is not enough to fully compensate drops.

26. The load current in a shunt generator is:

1. Ia - Ish
2. Ia + Ish
3. Only Ish
4. Zero always

Answer: A. Ia - Ish

Explanation: Armature current splits into load current and shunt field current.

27. In a shunt generator, armature current equals:

1. Load current plus shunt field current
2. Load current minus field current
3. Only field current
4. Zero

Answer: A. Load current plus shunt field current

Explanation: Ia = IL + Ish.

28. In a series generator, armature current is:

1. Equal to load current
2. Less than zero
3. Only shunt current
4. Independent of load

Answer: A. Equal to load current

Explanation: Series field, armature and load are in series.

29. In a DC generator, brush drop is generally due to:

1. Contact resistance at brush-commutator
2. Yoke flux only
3. Shaft length
4. Cooling air

Answer: A. Contact resistance at brush-commutator

Explanation: Voltage is lost at the sliding brush contact.

30. The main purpose of bearings is to:

1. Support rotating shaft
2. Produce flux
3. Convert AC to DC
4. Insulate commutator

Answer: A. Support rotating shaft

Explanation: Bearings support rotation and reduce friction.

31. The shaft of a DC generator is used to:

1. Transmit mechanical power
2. Insulate field coils
3. Collect current
4. Increase eddy currents

Answer: A. Transmit mechanical power

Explanation: The prime mover drives the armature through the shaft.

32. Cooling in DC machines is needed because:

1. Losses produce heat
2. Output is always zero
3. Commutator is non-metallic
4. Flux cannot exist

Answer: A. Losses produce heat

Explanation: Copper, iron and mechanical losses generate heat.

33. Slots in armature core are used to place:

1. Armature conductors
2. Field poles only
3. Bearings
4. Yoke bolts

Answer: A. Armature conductors

Explanation: Armature winding conductors are placed in slots.

34. Armature winding is generally a:

1. Closed winding
2. Open winding always
3. Single straight wire
4. Plastic ring

Answer: A. Closed winding

Explanation: DC armature winding forms a closed circuit through commutator connections.

35. Equalizer rings are mainly used with:

1. Lap winding
2. Wave winding only
3. Transformer winding
4. Single coil only

Answer: A. Lap winding

Explanation: Equalizer rings reduce circulating currents in lap-wound machines.

36. Dummy coils are used when:

1. Winding requirements need mechanical balance
2. No voltage is required
3. Brushes are absent
4. Poles are removed

Answer: A. Winding requirements need mechanical balance

Explanation: Dummy coils fill slots for balance but are not electrically active.

37. Pitch of armature winding is related to:

1. Distance between coil sides
2. Yoke thickness
3. Brush length
4. Bearing diameter

Answer: A. Distance between coil sides

Explanation: Coil pitch describes spacing between two sides of a coil.

38. Full-pitch coil spans:

1. One pole pitch
2. Half pole pitch
3. Zero pitch
4. Two shafts

Answer: A. One pole pitch

Explanation: Full-pitch coil sides are placed under opposite poles.

39. Short-pitch winding may be used to:

1. Reduce certain harmonics
2. Increase copper loss always
3. Remove commutator
4. Stop voltage generation

Answer: A. Reduce certain harmonics

Explanation: Short pitching can improve waveform and save copper.

40. In DC generator, frequency of induced emf in armature depends on:

1. Speed and number of poles
2. Brush material only
3. Load resistance only
4. Yoke paint

Answer: A. Speed and number of poles

Explanation: The rotating armature emf alternates before commutation.

41. Output of a DC generator is DC because of:

1. Commutator action
2. Transformer action
3. Bearing action
4. Yoke action only

Answer: A. Commutator action

Explanation: The commutator reverses coil connections to keep external polarity unidirectional.

42. A practical DC generator has ripple in output due to:

1. Finite number of commutator segments
2. No armature winding
3. No poles
4. Zero speed

Answer: A. Finite number of commutator segments

Explanation: More segments make output smoother but not perfectly ripple-free.

43. Increasing number of commutator segments generally:

1. Improves smoothness of DC output
2. Stops generation
3. Removes all losses
4. Reduces conductors to zero

Answer: A. Improves smoothness of DC output

Explanation: More segments reduce output pulsations.

44. The function of yoke includes:

1. Mechanical support and magnetic return path
2. Only collecting current
3. Only cooling water
4. Only reversing current

Answer: A. Mechanical support and magnetic return path

Explanation: Yoke holds poles and carries magnetic flux.

45. Pole core mainly carries:

1. Field winding
2. Brushes
3. Bearings
4. External load

Answer: A. Field winding

Explanation: Field coils are wound around pole cores.

46. Air gap should be kept small to:

1. Reduce magnetic reluctance
2. Increase noise only
3. Remove flux
4. Increase losses only

Answer: A. Reduce magnetic reluctance

Explanation: Smaller air gap helps magnetic flux pass more easily.

47. Too small air gap may cause:

1. Mechanical rubbing risk
2. No flux
3. Infinite efficiency
4. Zero armature current

Answer: A. Mechanical rubbing risk

Explanation: Mechanical clearance is also required between rotor and stator.

48. Magnetic saturation means:

1. Flux does not increase proportionally with field current
2. Resistance becomes zero
3. Machine stops instantly
4. Copper becomes mica

Answer: A. Flux does not increase proportionally with field current

Explanation: After saturation, extra field current gives smaller flux increase.

49. OCC curve bends at higher field current due to:

1. Magnetic saturation
2. Brush material
3. Load current only
4. Bearing friction

Answer: A. Magnetic saturation

Explanation: Iron saturation reduces the slope of the magnetization curve.

50. Armature reaction is more serious at:

1. High load current
2. No load
3. Zero armature current
4. Open circuit only

Answer: A. High load current

Explanation: Higher armature current produces stronger armature flux.

51. Demagnetizing effect of armature reaction tends to:

1. Reduce generated emf
2. Increase flux always
3. Remove losses
4. Increase speed

Answer: A. Reduce generated emf

Explanation: Reduced main flux lowers generated emf.

52. Cross-magnetizing effect of armature reaction:

1. Distorts flux distribution
2. Only reduces speed
3. Only cools machine
4. Converts DC to AC

Answer: A. Distorts flux distribution

Explanation: It shifts and distorts the main flux wave.

53. Reactance voltage during commutation is due to:

1. Inductance of short-circuited coil
2. Yoke friction
3. Brush weight only
4. Field resistance only

Answer: A. Inductance of short-circuited coil

Explanation: Changing current in an inductive coil induces reactance voltage.

54. High brush contact resistance may help commutation by:

1. Assisting current reversal
2. Increasing eddy currents
3. Removing magnetic field
4. Stopping rotation

Answer: A. Assisting current reversal

Explanation: Carbon brushes provide resistance that can aid current reversal.

55. Interpole polarity in generator is:

1. Same as next main pole in direction of rotation
2. Always north
3. Always south
4. No polarity

Answer: A. Same as next main pole in direction of rotation

Explanation: Generator interpole polarity is chosen to aid commutation correctly.

Advanced DC Generator MCQs

These questions are useful for deeper revision, numerical practice, interviews and competitive exams.

1. A generator rated 10 kW, 250 V has full-load current approximately:

1. 40 A
2. 4 A
3. 400 A
4. 0.04 A

Answer: A. 40 A

Explanation: Current = Power/Voltage = 10000/250 = 40 A.

2. If generated emf is 240 V and terminal voltage is 230 V, internal drop is:

1. 10 V
2. 470 V
3. 240 V
4. 0 V

Answer: A. 10 V

Explanation: Internal voltage drop is 240 - 230 = 10 V.

3. If a 220 V generator supplies 20 A, output power is:

1. 4.4 kW
2. 11 W
3. 240 W
4. 0.11 kW

Answer: A. 4.4 kW

Explanation: Output power = VI = 220 × 20 = 4400 W.

4. If armature current is 50 A and armature resistance is 0.1 Ω, armature copper loss is:

1. 250 W
2. 5 W
3. 50 W
4. 5000 W

Answer: A. 250 W

Explanation: Copper loss = I²R = 50² × 0.1 = 250 W.

5. If speed of a DC generator is doubled and flux is constant, generated emf:

1. Doubles
2. Halves
3. Becomes zero
4. Remains always same

Answer: A. Doubles

Explanation: Generated emf is directly proportional to speed.

6. If flux per pole is reduced by half at same speed, generated emf:

1. Becomes half
2. Doubles
3. Becomes infinite
4. Does not change

Answer: A. Becomes half

Explanation: EMF is directly proportional to flux per pole.

7. A 4-pole lap-wound generator has parallel paths:

1. 4
2. 2
3. 8
4. 1

Answer: A. 4

Explanation: For simplex lap winding, A = P = 4.

8. A 6-pole simplex wave-wound generator has parallel paths:

1. 2
2. 6
3. 12
4. 3

Answer: A. 2

Explanation: For simplex wave winding, A = 2.

9. For same conductors and speed, wave winding gives higher voltage because:

1. It has fewer parallel paths
2. It has no flux
3. It has no commutator
4. It has more brush loss

Answer: A. It has fewer parallel paths

Explanation: Fewer parallel paths mean more series conductors per path.

10. If field current is increased before saturation, generated emf:

1. Increases
2. Decreases to zero
3. Becomes AC only
4. Unaffected always

Answer: A. Increases

Explanation: Higher field current increases flux and hence emf.

11. A DC generator running without load has armature current approximately equal to:

1. Shunt field current in shunt generator
2. Full-load current
3. Short-circuit current
4. Infinite current

Answer: A. Shunt field current in shunt generator

Explanation: At no-load, output current is nearly zero, but shunt field current exists.

12. Which generator is suitable for battery charging with rising voltage behavior?

1. Series generator may be used with control
2. Differential compound only
3. No generator
4. Only AC alternator

Answer: A. Series generator may be used with control

Explanation: Series generator voltage rises with load current, but practical charging needs control.

13. Which DC generator is commonly used where constant voltage is required?

1. Shunt or cumulative compound generator
2. Differential compound only
3. Series generator only
4. No-load generator

Answer: A. Shunt or cumulative compound generator

Explanation: Shunt and compound generators can provide reasonably constant voltage.

14. For long feeders, compound generators may be used to:

1. Compensate line voltage drop
2. Increase bearing friction
3. Remove commutator
4. Make AC output

Answer: A. Compensate line voltage drop

Explanation: Over-compounding can help maintain voltage at the load end.

15. In a DC generator, load increase usually increases:

1. Armature current
2. Yoke thickness
3. Number of poles
4. Commutator segments

Answer: A. Armature current

Explanation: More load draws more current from the armature.

16. Which loss varies strongly with load current?

1. Armature copper loss
2. Friction loss
3. Windage loss
4. Core loss at constant speed

Answer: A. Armature copper loss

Explanation: Armature copper loss is proportional to I².

17. Which losses are nearly constant at constant speed and field?

1. Iron, friction and windage losses
2. Armature copper loss only
3. Load copper loss only
4. Short-circuit loss only

Answer: A. Iron, friction and windage losses

Explanation: These losses are less dependent on load current.

18. The best location for carbon brushes is adjusted to reduce:

1. Sparking
2. Yoke weight
3. Shaft length
4. Air gap flux to zero

Answer: A. Sparking

Explanation: Correct brush position improves commutation.

19. A generator commutator should have:

1. Smooth surface and proper insulation
2. Broken segments
3. Oil film everywhere
4. Loose connections

Answer: A. Smooth surface and proper insulation

Explanation: Good commutator condition improves current collection.

20. Excessive sparking can damage:

1. Commutator and brushes
2. Yoke paint only
3. Foundation only
4. Cooling fan only

Answer: A. Commutator and brushes

Explanation: Sparking causes heating, pitting and wear.

21. A DC generator nameplate usually provides:

1. Voltage, current, power and speed ratings
2. Only color
3. Only shaft length
4. Only bearing brand

Answer: A. Voltage, current, power and speed ratings

Explanation: Ratings tell safe operating limits.

22. Overloading a DC generator causes:

1. Excessive heating
2. Zero current
3. No copper loss
4. Automatic efficiency 100%

Answer: A. Excessive heating

Explanation: Higher current increases copper losses and temperature.

23. A fuse or circuit breaker is used for:

1. Protection against excessive current
2. Increasing flux
3. Commutation
4. Lamination

Answer: A. Protection against excessive current

Explanation: Protection devices disconnect unsafe currents.

24. DC generators require maintenance mainly because of:

1. Brushes and commutator
2. No moving parts
3. No contact surfaces
4. Absence of losses

Answer: A. Brushes and commutator

Explanation: Sliding contacts wear with time.

25. Compared with alternators, DC generators are less common in modern large power generation because:

1. AC is easier to transform and transmit
2. DC cannot be generated
3. DC has no use
4. Alternators have no losses

Answer: A. AC is easier to transform and transmit

Explanation: AC voltage transformation makes transmission easier.

26. DC generators are still useful for:

1. Battery charging, labs and special DC supplies
2. Only household AC sockets
3. Only microwave ovens
4. No application

Answer: A. Battery charging, labs and special DC supplies

Explanation: They are used where controlled DC power is required.

27. The induced emf in each armature conductor is alternating in nature before commutation because:

1. Conductor passes under alternate poles
2. Brushes are fixed
3. Yoke is round
4. Field current is zero

Answer: A. Conductor passes under alternate poles

Explanation: As conductors move under N and S poles, emf direction reverses.

28. Commutator converts internal AC to external DC by:

1. Reversing connections at proper instant
2. Increasing resistance only
3. Reducing speed
4. Changing copper to mica

Answer: A. Reversing connections at proper instant

Explanation: It mechanically rectifies the armature emf.

29. The polarity of generated voltage depends on:

1. Direction of rotation and field polarity
2. Yoke weight only
3. Brush size only
4. Bearing oil

Answer: A. Direction of rotation and field polarity

Explanation: Changing rotation or field polarity can reverse output polarity.

30. If both field polarity and direction of rotation are reversed, generated voltage polarity:

1. May remain same
2. Always becomes zero
3. Always doubles
4. Cannot be predicted at all

Answer: A. May remain same

Explanation: Reversing both factors cancels the polarity reversal effect.

31. In Fleming’s right-hand rule, thumb indicates:

1. Motion of conductor
2. Magnetic field
3. Induced current
4. Resistance

Answer: A. Motion of conductor

Explanation: Thumb represents motion, forefinger field and middle finger induced current/emf.

32. In Fleming’s right-hand rule, forefinger indicates:

1. Magnetic field
2. Motion
3. Current only
4. Speed

Answer: A. Magnetic field

Explanation: Forefinger points in the direction of magnetic field.

33. In Fleming’s right-hand rule, middle finger indicates:

1. Induced current or emf
2. Flux
3. Motion
4. Force

Answer: A. Induced current or emf

Explanation: Middle finger gives induced current/emf direction.

34. The main function of a generator is opposite to that of a motor because generator:

1. Converts mechanical to electrical energy
2. Converts electrical to mechanical energy
3. Stores energy only
4. Converts AC to heat only

Answer: A. Converts mechanical to electrical energy

Explanation: A motor consumes electrical energy, while a generator produces it from mechanical input.

35. A DC motor and DC generator are similar in:

1. Basic construction
2. Energy conversion direction
3. Input source always
4. Output only

Answer: A. Basic construction

Explanation: The same DC machine can often work as motor or generator with suitable conditions.

36. The field current in a shunt generator is small because field winding has:

1. High resistance and many turns
2. Very low resistance and few turns
3. No turns
4. Only one copper bar

Answer: A. High resistance and many turns

Explanation: Shunt field is connected across voltage and is designed for small current.

37. The series field winding has low resistance because it carries:

1. Load current
2. Only leakage current
3. No current
4. Only eddy current

Answer: A. Load current

Explanation: Series winding uses thick conductors to carry load current.

38. The function of field rheostat in a shunt generator is to control:

1. Field current and terminal voltage
2. Shaft weight
3. Brush material
4. Air gap length

Answer: A. Field current and terminal voltage

Explanation: Changing field current changes flux and output voltage.

39. If field resistance is increased in a shunt generator, field current usually:

1. Decreases
2. Increases infinitely
3. Becomes AC
4. Unaffected always

Answer: A. Decreases

Explanation: By Ohm’s law, higher resistance reduces shunt field current.

40. The polarity of interpoles must be correct to:

1. Neutralize reactance voltage
2. Increase friction
3. Reduce shaft speed only
4. Remove armature winding

Answer: A. Neutralize reactance voltage

Explanation: Wrong interpole polarity worsens sparking.

41. In DC generator testing, load test helps find:

1. Voltage regulation and efficiency
2. Only lamination thickness
3. Only brush color
4. Only shaft diameter

Answer: A. Voltage regulation and efficiency

Explanation: Load test observes performance under actual load.

42. Swinburne’s test is commonly used for:

1. Efficiency estimation of DC shunt machines
2. Short circuit test of transformer only
3. Finding pole pitch only
4. Measuring brush length

Answer: A. Efficiency estimation of DC shunt machines

Explanation: It estimates losses and efficiency without full-load test.

43. Hopkinson’s test is also called:

1. Regenerative test
2. Open circuit test only
3. Blocked rotor test
4. No-load test of transformer

Answer: A. Regenerative test

Explanation: Two similar DC machines are tested regeneratively.

44. Stray load losses are due to:

1. Leakage flux and load-dependent effects
2. Only bearing friction
3. Only windage
4. Only field copper

Answer: A. Leakage flux and load-dependent effects

Explanation: They occur because practical flux and current distributions are not ideal.

45. Brush contact loss is approximately:

1. Brush drop times armature current
2. Speed divided by flux
3. Flux times poles only
4. Resistance divided by current

Answer: A. Brush drop times armature current

Explanation: Power lost at brushes is voltage drop multiplied by current.

46. The armature core is cylindrical to:

1. Allow smooth rotation in magnetic field
2. Increase brush wear
3. Remove slots
4. Stop flux

Answer: A. Allow smooth rotation in magnetic field

Explanation: A cylindrical rotor provides uniform mechanical rotation.

47. The commutator is mounted on:

1. Shaft
2. Yoke
3. Pole shoe
4. Field winding

Answer: A. Shaft

Explanation: The commutator rotates with the armature on the shaft.

48. In DC generator, the number of commutator segments is generally equal to:

1. Number of armature coils
2. Number of poles only
3. Number of brushes only
4. Number of bearings

Answer: A. Number of armature coils

Explanation: Each coil is connected to commutator segments.

49. The most suitable answer for why mica is used in commutator is:

1. Good insulation and heat resistance
2. Low conductivity
3. Magnetic strength
4. Lubrication

Answer: A. Good insulation and heat resistance

Explanation: Mica withstands heat and insulates copper segments.

50. Undercutting of mica in commutator is done because:

1. Mica is harder than copper and may protrude
2. Copper is insulation
3. Brushes need oil
4. Flux must increase

Answer: A. Mica is harder than copper and may protrude

Explanation: Mica is recessed so brushes contact copper properly.

51. The purpose of brush spring pressure is to:

1. Maintain proper contact
2. Increase field flux directly
3. Reduce armature conductors
4. Change winding type

Answer: A. Maintain proper contact

Explanation: Correct pressure prevents loose contact and excessive wear.

52. Too much brush pressure causes:

1. Excessive wear and friction
2. No contact
3. Zero heating always
4. No loss

Answer: A. Excessive wear and friction

Explanation: High pressure increases mechanical loss and brush wear.

53. Too little brush pressure may cause:

1. Sparking
2. Better efficiency always
3. No voltage drop
4. No contact loss

Answer: A. Sparking

Explanation: Poor contact causes sparking and unstable current collection.

Quick Answer Key

Question No.	Correct Answer
1	B. DC electrical energy
2	B. Faraday’s law of electromagnetic induction
3	B. Fleming’s right-hand rule
4	B. Stator
5	C. Armature
6	A. Yoke
7	B. Magnetic field
8	B. Copper
9	B. Eddy current loss
10	A. Silicon steel
11	B. Mechanical rectifier
12	C. Commutator
13	B. Carbon or graphite
14	B. Spread flux uniformly
15	B. Mechanical input
16	C. Flux and speed
17	B. Pole shoe and armature
18	A. Induced emf
19	A. Copper
20	B. Mica
21	B. Brushes
22	B. Field poles
23	B. An external DC source
24	A. Residual magnetism
25	B. In parallel with armature
26	B. In series with armature and load
27	C. Both series and shunt fields
28	B. Assists shunt field
29	B. Opposes shunt field
30	A. E = PΦZN/60A
31	A. Flux per pole
32	B. Number of armature conductors
33	B. Parallel paths in armature
34	B. P
35	A. 2
36	B. Low voltage, high current
37	B. High voltage, low current
38	A. IaRa
39	A. Voltage drops
40	B. Armature current
41	B. Distort and weaken main flux
42	A. Armature reaction
43	A. Magnetic neutral axis
44	B. Reversal of current in a coil under brush
45	A. Sparking at brushes
46	B. Commutation
47	A. Armature
48	B. Pole faces
49	B. Large machines with heavy load changes
50	B. Using laminated core
51	A. Magnetic material and flux density
52	A. Resistance of windings
53	A. Friction and windage
54	A. Core losses
55	A. Output/Input
56	A. Constant loss
57	B. Terminal voltage from no-load to full-load
58	B. Low voltage drop and good regulation
59	A. Open circuit characteristic
60	A. Constant speed
61	A. Self-excited generator voltage build-up
62	A. Voltage build-up in shunt generator
63	A. Voltage build-up at given field resistance
64	A. Residual magnetism is lost
65	A. Voltage may not build up
66	A. Residual magnetism
67	A. Generated emf and armature current
68	A. Terminal voltage and load current
69	A. Armature drop and armature reaction
70	A. Series field flux increases
71	A. Armature resistance drop
72	A. Better voltage regulation
73	A. Higher than no-load voltage
74	A. Nearly constant terminal voltage
75	A. Less than no-load voltage
76	A. Ia - Ish
77	A. Load current plus shunt field current
78	A. Equal to load current
79	A. Contact resistance at brush-commutator
80	A. Support rotating shaft
81	A. Transmit mechanical power
82	A. Losses produce heat
83	A. Armature conductors
84	A. Closed winding
85	A. Lap winding
86	A. Winding requirements need mechanical balance
87	A. Distance between coil sides
88	A. One pole pitch
89	A. Reduce certain harmonics
90	A. Speed and number of poles
91	A. Commutator action
92	A. Finite number of commutator segments
93	A. Improves smoothness of DC output
94	A. Mechanical support and magnetic return path
95	A. Field winding
96	A. Reduce magnetic reluctance
97	A. Mechanical rubbing risk
98	A. Flux does not increase proportionally with field current
99	A. Magnetic saturation
100	A. High load current
101	A. Reduce generated emf
102	A. Distorts flux distribution
103	A. Inductance of short-circuited coil
104	A. Assisting current reversal
105	A. Same as next main pole in direction of rotation
106	A. 40 A
107	A. 10 V
108	A. 4.4 kW
109	A. 250 W
110	A. Doubles
111	A. Becomes half
112	A. 4
113	A. 2
114	A. It has fewer parallel paths
115	A. Increases
116	A. Shunt field current in shunt generator
117	A. Series generator may be used with control
118	A. Shunt or cumulative compound generator
119	A. Compensate line voltage drop
120	A. Armature current
121	A. Armature copper loss
122	A. Iron, friction and windage losses
123	A. Sparking
124	A. Smooth surface and proper insulation
125	A. Commutator and brushes
126	A. Voltage, current, power and speed ratings
127	A. Excessive heating
128	A. Protection against excessive current
129	A. Brushes and commutator
130	A. AC is easier to transform and transmit
131	A. Battery charging, labs and special DC supplies
132	A. Conductor passes under alternate poles
133	A. Reversing connections at proper instant
134	A. Direction of rotation and field polarity
135	A. May remain same
136	A. Motion of conductor
137	A. Magnetic field
138	A. Induced current or emf
139	A. Converts mechanical to electrical energy
140	A. Basic construction
141	A. High resistance and many turns
142	A. Load current
143	A. Field current and terminal voltage
144	A. Decreases
145	A. Neutralize reactance voltage
146	A. Voltage regulation and efficiency
147	A. Efficiency estimation of DC shunt machines
148	A. Regenerative test
149	A. Leakage flux and load-dependent effects
150	A. Brush drop times armature current
151	A. Allow smooth rotation in magnetic field
152	A. Shaft
153	A. Number of armature coils
154	A. Good insulation and heat resistance
155	A. Mica is harder than copper and may protrude
156	A. Maintain proper contact
157	A. Excessive wear and friction
158	A. Sparking

Frequently Asked Questions on DC Generator

What is a DC generator?

A DC generator is an electrical machine that converts mechanical energy into direct current electrical energy.

Which rule is used in DC generator?

Fleming’s right-hand rule is used to determine the direction of induced emf in a DC generator.

Why is the armature core laminated?

The armature core is laminated to reduce eddy current loss and improve the efficiency of the machine.

What is the function of the commutator?

The commutator converts the alternating emf generated inside the armature into unidirectional DC output at the terminals.

What is armature reaction?

Armature reaction is the effect of armature current on the main field flux. It distorts and may weaken the main magnetic field.

Which DC generator gives nearly constant voltage?

A shunt generator or a cumulative compound generator is commonly used where nearly constant voltage is required.

Conclusion

These DC Generator MCQ questions are useful for quick revision and exam preparation. If you are preparing for electrical engineering exams, diploma exams, ITI exams, SSC JE, RRB JE, GATE basics or technical interviews, revise the construction, working principle, armature reaction, commutation, losses and generator characteristics carefully.

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